Getting old and does it matter what I eat?

I've been writing this blog for so long that I'm not sure if I'm repeating myself but here goes anyway....
Now that I'm officially OLD (65), I'm beginning to wonder (again, I apologize if I wondered this in the blog before) if it really matters how I eat or how much I weigh. Here's the thing. Isn't the damage already done? Haven't I breathed in enough crap, eaten enough pesticide and deposited enough toxins to do me in? Does it really make a difference if I eat a bushel of blueberries right now? Will that improve my memory? If I lose 20 pounds (in my dreams), will I avoid breast cancer? I know that eating oatmeal might reduce my cholesterol but my arteries are already loaded with plaque both from years of abuse and because it's just a natural consequence of aging.
Speaking of which....I am getting old. Sure. I could live another 30 plus years. But most of my life is behind me. So far behind that I need my glasses to see it!
So, does it matter? Will I live one day longer if I have oatmeal AND blueberries for breakfast? I've eaten a pretty healthy diet my whole life...just way too much of it. I've always eaten fruits and veggies. Of course, they've often been topped with sugar and cooked in fat but that doesn't negate the antioxidants contained therein!
This is a serious concern for me. Something for me to ponder over the next few weeks. When, if at all, does it stop being important to eat a healthy diet? When, if at all, does it matter what you weigh?